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---
language: Objective-C
contributors:
- ["Eugene Yagrushkin", "www.about.me/yagrushkin"]
- ["Yannick Loriot", "https://github.com/YannickL"]
filename: LearnObjectiveC.m
---
Objective-C is the main programming language used by Apple for the OS X and iOS operating systems and their respective frameworks, Cocoa and Cocoa Touch.
It is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.
```Objective-C
// Single-line comments start with //
/*
Multi-line comments look like this.
*/
// Imports the Foundation headers with #import
#import <Foundation/Foundation.h>
// Your program's entry point is a function called
// main with an integer return type.
int main (int argc, const char * argv[])
{
// Create an autorelease pool to manage the memory into your program
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// Print "Hello World!" to the console
NSLog(@"Hello World!");
// Clean up the memory you used into your program
[pool drain];
// End your program
return 0;
}
// all the primitive variable types are the same as in C
// char, int, long, double, float
// Simple, common classes
// number
NSNumber *firstNumber = @1;
NSNumber *secondNumber = @23.0;
NSNumber *boolNumber = @YES;
// string
NSString *aString = @"some string";
// array
NSArray *array = @[ @1, @2];
// dictionary
NSDictionay *dictionary = @{ @"aKey" : @"aValue", @"aKey2" : @"aValue2" };
// Import headers with #import
#import <UIKit/UIKit.h>
#import "SomeAppDelegate.h"
##Coding classes
// Declare your class in a header(.h) file:
@interface UserObject : NSObject{
// instance variables
}
// Class method
+ (NSString*) ClassMethod;
// Instance method
- (NSString*) instanceMethodWithParmeter:(NSString*)string;
@end
// Add class methods in an implementation (.m) file:
@implementation UserObject
+ (NSString*) ClassMethod{
return @"SomeString";
}
- (NSString*) instanceMethodWithParmeter:(NSString*)string;
{
return @"New string";
}
- (NSString*) otherMethodWithString:(NSString*)string;
{
return [NSString stringWithString:string];
}
@end
// Create an object instance by allocating memory and initializing it. An object is not fully functional until both steps have been completed.
UserObject *someObject = [[UserObject alloc] init];
##Calling Methods
// The Objective-C model of object-oriented programming is based on message passing to object instances.
// In Objective-C one does not simply call a method; one sends a message.
[someObject instanceMethodWithParmeter:@"Steve Jobs"];
##Nested Messages
// nested messages look like this:
[someObject instanceMethodWithParmeter:[someObject otherMethodWithString:@"Jony Ive"]];
```
## Further Reading
[Wikipedia Objective-C](http://en.wikipedia.org/wiki/Objective-C)
[Learning Objective-C](http://developer.apple.com/library/ios/referencelibrary/GettingStarted/Learning_Objective-C_A_Primer/)
[iOS For High School Students: Getting Started](http://www.raywenderlich.com/5600/ios-for-high-school-students-getting-started)
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